New Chicks today

I bought 4 Australorp chicks today which earned me 2 free ones! So I brought them home and put them right under my broody Buff Orpington hen. I did this last year with 2 chicks and it worked out great. She kind of "growled" and tried to peck at them for a couple of minutes, I shielded them with my hand and pushed them all under her. After about 5 minutes she started making little clucking noises and looked very happy. I stayed with them for about 30 minutes and they seem just fine. I have to pick her up and put her out by the feed and water so the chicks can get some and then I pick her up and put her back in the nest. She won't budge on her own! I will do this for a couple of days till she starts coming out by herself. She is a very good mother hen!